The major devices in integrated circuits (ICs), especially very-large-scale-integration (VLSI), include metal-oxide-semiconductor field-effect transistors (MOS transistors). With the continuous developments of the IC manufacturing, technology, the technical node of the semiconductor device technology has become smaller and the smaller; and the geometric dimension of the semiconductor structures has become smaller and smaller by following the Moore's law. When the size of the semiconductor devices is reduced to a certain extent, secondary effects caused by the physical limitations of the semiconductor structures successively emerge. Accordingly, the critical dimension reduction in proportion of the semiconductor structures has become more and more difficult. One of the most challenging issues in the field of semiconductor manufacturing is about the large leakage current problem in the semiconductor structures, which is mainly caused by the continuous reduction of the thickness of the conventional gate dielectric layer.
The current approach to solve such issues is to replace the conventional silicon dioxide gate dielectric material with a high-K dielectric material; and use a metal material as the gate electrode. Such a conventional method may avoid the Femi level pin effect and the boron diffusion effect of the high-K material and the conventional gate material. The inclusion of the high-K metal gate (HKMG) reduces the leakage current of the semiconductor structures.
Although the introduction of the HKMG structures is able to improve the electrical properties of the semiconductor structures to a certain extent, the semiconductor devices formed by the existing methods may need further improvements. The disclosed semiconductor structures and methods are directed to solve one or more problems set forth above and other problems in the art.